The present invention generally relates to an optical disk drive for reading out information from a disk by irradiating a converged light beam onto the disk. More particularly, the present invention relates to the generation of a read clock signal used as a reference in reading data.
An optical disk, on which video information, computer data or the like has been recorded, is used widely as one of storage media of various types. In recent years, an optical disk is increasingly required to read out data and perform a seek operation at higher speeds.
While a tracking control is enabled, an optical disk drive reads out information from a read-only disk like a CD or DVD-ROM, and a read clock signal is controlled to have the phase thereof locked onto that of an RF signal resulting from light reflected from the disk. During a seek operation on the other hand, the optical disk drive moves a head unit toward the inner or outer periphery of the disk with the tracking control disabled. In such a state, the optical disk drive controls the ratio of the frequency of the read clock signal to that of a particular pattern included in the RF signal at a constant value.
In the conventional optical disk drive, however, if the seek speed is high, then the operation of detecting the particular pattern is disturbed or the response of a disk motor is delayed. Accordingly, the frequency of the read clock signal greatly deviates from a desired one, and therefore the phase locking control cannot be started as soon as the seek operation is finished. As a result, the start of data reading is adversely delayed.
Also, in reading out data from a recordable disk such as a DVD-RAM or DVD-R, the RF signal cannot be used because data does not exist on each and every track. Accordingly, while a data unrecorded area of the disk is being irradiated with a light beam, the frequency of the read clock signal cannot be fixed.
An object of the present invention is getting data reading started as soon as possible after a head has reached a position over a desired track on an optical disk through the seek operation.
Another object of the present invention is getting the frequency of a read clock signal fixed even when there is a data unrecorded area on a recordable disk.
An optical disk drive according to the present invention is adapted to read out information from a disk by irradiating a converged light beam onto the disk. The optical disk drive includes: means for rotating the disk; means for converting light reflected off the disk into an electric signal; clock generating means for generating a read clock signal with a variable frequency; phase locking control means for controlling the clock generating means in such a manner as to lock the phase of the read clock signal onto that of the electric signal; means for moving the light beam toward a target track on the disk; frequency control means for controlling the clock generating means in such a manner as to equalize the frequency of the read clock signal with a frequency expected at the target track; and switching means for deactivating the phase locking control means and activating the frequency control means at least just before the light beam has reached the target track.
Another optical disk drive according to the present invention is adapted to read out information from a disk, which includes a plurality of data portions and address portions, by irradiating a converged light beam onto the disk. Each said data portion has recordable wobbling tracks, while each said address portion is located between an adjacent pair of the data portions. An address has been recorded in advance on each said address portion. The optical disk drive includes: means for rotating the disk; means for converting light reflected off the disk into an electric signal; means for detecting a frequency of a wobbling component from the electric signal, the wobbling component corresponding to the shape of the tracks in each said data portion; clock generating means for generating a read clock signal with a variable frequency; phase locking control means for controlling the clock generating means in such a manner as to lock the phase of the read clock signal onto that of the electric signal; frequency control means for controlling the clock generating means such that a ratio of the frequency of the read clock signal to the detected frequency of the wobbling component becomes a constant value; and switching means for activating the phase locking control means while each said address portion is being irradiated with the light beam and for activating the frequency control means while each said data portion is being irradiated with the light beam.